PAllison drove home at 58 mph, but her brother Austin, who left at the same time, could drive at only 40 mph. When Allison arrived, Austin still had 90 miles to go. How far did Allison drive?
miles
Please help I'm taking a test

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.